In order to standardize the standards for textile color evaluation, the textile printing and dyeing industry needs to use special Color measuring card. Today, the printing and dyeing people will talk about the standard of color cards for judging the color difference of textiles, the use of color measuring cards, and several factors that affect color.
01 Textile Color Measurement Color Card Standard
In the national standard GB 250-2008, the basic method for judging the color difference of textiles is clearly defined. The standard stipulates that the color difference is divided into 5 levels and 9 levels, of which level 5 is the best and level 1 is the worst. The 5-level and 9-level standards are set as follows: Level 1, Level 1-2, Level 2, Level 2-3, Level 3, Level 3-4, Level 4, Level 4-5, Level 5. In dyeing factories, the levels between Level 4 and Level 5 are also called Level 4 and a half or Level 4.5.
In order to accurately judge the color differences between textiles, the national standard GB 250-2008 is also equipped with a gray sample card. The gray sample card is referred to as the gray card and consists of three parts: the gray card outer sleeve, the gray card inner sleeve and the gray card. The gray card jacket is used to store the gray card and is generally made of plastic. The inner sleeve of the gray card and the gray card itself constitute the main part of the gray card. The inner sleeve of the gray card is an iron-gray paper object with a square hole in the middle. The gray card itself can slide manually in the direction of the inner extension of the inner sleeve.
02 How to use color measuring cards
When comparing color differences, The gray card needs to be placed horizontally. The different levels of color differences presented by the gray card itself can be seen in the middle opening of the gray card inner sleeve. The sample cards to be tested are placed side by side in the middle and lower part of the gray card jacket.
When the color difference in the square hole of the jacket is close to or consistent with the color difference between the tested samples, the color difference between the tested colors can be judged.
In order to protect the gray card, it is strictly forbidden to touch the surface of the gray card inside the square hole with your fingers to avoid gradual corrosion of the gray card surface. The gray card itself is also made of iron-gray paper material, and each level of color difference is marked by dark gray and light gray. As the color difference increases, the depth difference between dark gray and light gray becomes larger and larger.
Usually, the color difference of textiles mainly includes head and tail difference, front and rear difference, left, middle and right color difference, cylinder difference, tube difference, match difference, etc. The head-to-tail difference refers to the color difference between the head and the tail of the long pad-dyed fabric, which generally requires no less than level 4.
The difference between the front-end and back-end colors of each color is called the front-to-back difference, and the requirement is also level 4. The color difference between different numbers is called match difference, and the requirement should not be lower than level 4. Within the entire fabric, the color difference between the left, middle and right parts is called the left, middle and right color difference. Customers generally require no less than level 4.5. The color difference between cylinders of the same color must not be less than 4 levels.
The color difference between the two dyeing tubes formed after one-tank double-tube dyeing equipment dyes fabrics is called tube difference, and the tube difference is usually required to be no less than 4.5.
03 Impact on textile color measurement Accuracy factors
For printing and dyeing manufacturers, there are many factors in life that affect the accuracy of textile color measurement. These are summarized in the following aspects.
Moisture content
Measurement of moisture in the fabric to be tested The color results will be greatly affected, so the sample needs to be humidified to make its moisture content relatively stable. Humidification should be carried out in a room with constant temperature and humidity to ensure that all samples have enough time to reach a constant moisture content.
Among them, the humidity control time of most highly hygroscopic fabrics takes several hours. In addition, environmental conditions will also affect the moisture content of the sample. During the measurement period, the humidity of the sample should be maintained as much as possible. (Especially in autumn, the ambient humidity will decrease significantly. Appropriately increasing the humidity is very helpful for the accuracy and consistency of the color of the instrument; the relative humidity required by general brands is 65%.)
Transparency
Most fabrics are transparent to some extent and therefore should be tested in layers until it becomes opaque. The measurement results after placing a white board and a black board on the back of the laminated sample are the same, indicating that the number of folded layers is sufficient.
If the use of multiple layers of soft materials causes other problems, a fixed number of white materials or porcelain plates without fluorescent whitening agents can be lined on the back. Generally, the same backing as the sample is used. Lining material.
Fluorescence
Usually a light source can be inserted between the light source and the sample. Filters that absorb UV light to effectively eliminate UV light that can cause fluorescence, but using this method may cause results that are inconsistent with visual inspection. Therefore, this method can only be used in situations where UV radiation adsorption causes fluorescence.
Although instruments that control UV light energy produce results consistent with visual inspection, these results are difficult to reproduce on non-similar instruments. When the sample strip has fluorescent properties, all samples for comparison should be measured at the same time interval (within 1 hour), and pre-measured data (standards and samples) cannot be used as a basis for comparison.
Stiffness
When the fabric is soft, the sample is extremely It is easy to extend into the light-transmitting hole of the tester, thus affecting the test results.�Results. The sample to be measured should be flat, with a rigid structure on the back and sufficient thickness to eliminate the influence of transparency factors; some samples, especially fibers and yarns, can be measured behind glass when measuring color with a spectrophotometer. Improve measurement reproducibility.
Sensitivity to light and heat
To light or heat Sensitive specimens are best measured in a moment-exposure colorimeter. Flash instruments and instruments with automatic shutters can provide time-limited mechanisms for specimen exposure. When measuring these samples, do not use instruments that scan visible light (it takes several seconds to complete a unit measurement). The overall specimen preparation should include protective measures to limit the exposure of the specimen before measurement. Instruments that illuminate the specimen in a single color are also suitable for measuring these similar specimens.
Small area sample
Needed to be used on the colorimeter For small samples under observation in a small area, the average of multiple measurement results should be read in order to improve measurement accuracy. Samples smaller than the observation area of the instrument cannot be measured.
Surface structure of the sample
Appearance color separation ability of the instrument An advantage in dye formulation and a disadvantage in quality control applications. When measuring only the color of a specimen, the most effective method is to place the specimen behind glass and then apply sufficient pressure to eliminate differences in surface structure.
The same measures and conditions should be adopted when glass is used for non-stiff specimens. When surface structure causes orientation changes, the number of measurements on the specimen can be determined as a multiple of 4, rotated 90 degrees after each measurement, and then average all measurements to produce a single set of colorimetric values.
Color uniformity
When the color of the measured sample is uneven When measuring, an average value (the average of spectral data from a spectrophotometer or tristimulus data from a colorimeter) needs to be determined to achieve consistent, reproducible measurement results. This requires measuring a large amount of data to select the window. When the test is repeated at any location on the specimen, the average number shall be reproducible. </p
